The existing equipment used for medical (and dental) x-ray radiography contains high voltage vacuum tubes and produce x-rays as a result of the bombardment of a target by electrostatically accelerated electrons. The electrical supplies for such tubes are based on high voltage (.about.100 kilivolts) transformers. These transformers are very heavy, cumbersome, dangerous, and expensive pieces of equipment. Such conventional x-ray medical radiograph equipment is not portable and thus limits the use of the x-ray radiography in ambulances, distant areas, etc.
U.S. Pat. No. 5,323,442, filed Feb. 28, 1992, which is commonly assigned to the assignee of this patent document, the disclosure of which is incorporated herein by reference, describes an x-ray source that is based on an Electron Cyclotron Resonance (ECR) plasma. The ECR x-ray source is quite convenient to be used as a light, compact, safe and inexpensive low-voltage (but high enough photon energy and intensity) x-ray source. However, that ECR x-ray source has a large x-ray emitting surface which makes the resolution of the x-ray image poor and, without modification, not reasonably practicable for x-ray radiography, particularly in the medical field.
There remains a continuing need for better sources of x-rays for radiography. There also is a need for economical x-ray sources having sufficient intensity for radiography that are lightweight, portable, and may be operated from conventional energy supplies.